This invention relates to a process to produce propylene from a hydrocarbon feed stream containing C5""s and/or C6""s, preferably a naphtha feed stream, where multiple feeds are used to feed portions of the feed stream into different portions of the reactor, or into different reactors.
Propylene is an important chemical of commerce. In general propylene is largely derived from selected petroleum feed materials by procedures such as steam cracking which also produces high quantities of other materials. At times, there exists shortages of propylene which result in uncertainties in feed supplies, rapidly escalating raw material costs and similar situations which are undesirable from a commercial standpoint. Also due to imbalances in hydrocarbon values, economics favor using alternate feedstocks provided an effective process for forming propylene was available. Methods are known for the conversion of higher hydrocarbons to reaction mixtures comprised of the C2 and C3 lighter olefins. For example, EP 0 109 059 A and EP 0 109 060 A provide illustrative disclosures of conditions and catalysts which are effective for the conversion of higher hydrocarbons such as butenes to the lighter olefins. U.S. Ser. No. 07/343,097 likewise is believed to provide a detailed disclosure of prior methods for the production of lower olefins from higher hydrocarbon feed materials. In certain instances, it would be very advantageous to provide means for still further improving yields of propylene which result from the conversion of less expensive higher hydrocarbon feed materials.
Prior methods to produce propylene include:
1. The disproportionation or metathesis of olefins. See for example U.S. Pat. Nos. 3,261,879; 3,883,606; 3,915,897; 3,952,070; 4,180,524; 4,431,855; 4,499,328; 4,504,694; 4,517,401; 4,547,617.
2. U.S. Pat. No. 5,026,936 which discloses the selective production of propylene for C4 and higher hydrocarbons by reacting the feed with a zeolite, then the ethylene produced is passed to a metathesis zones where it is further converted to propylene. See also, U.S. Pat. Nos. 5,026,935; 5,171,921 and 5,043,522.
3. U.S. Pat. No. 5,043,522 which discloses using ZSM-5 with C4+ feeds to produce lighter olefins including propylene.
4. U.S. Pat. No. 4,830,728 discloses a fluid catalytic cracking (FCC) unit that is operated to maximize olefin production. The FCC unit has two separate risers into which a different feed stream is introduced. The operation of the risers is designed so that a suitable catalyst will act to convert a heavy gas oil in one riser and another suitable catalyst will act to crack a lighter olefin/naphtha feed in the other riser. Conditions within the heavy gas oil riser can be modified to maximize either gasoline or olefin production. The primary means of maximizing production of the desired product is by using a specified catalyst.
5. U.S. Pat. No. 5,069,776 teaches a process for the conversion of a hydrocarbonaceous feedstock by contacting the feedstock with a moving bed of a zeolitic catalyst comprising a zeolite with a pore diameter of 0.3 to 0.7 nm, at a temperature above about 500xc2x0 C. and at a residence time less than about 10 seconds. Olefins are produced with relatively little saturated gaseous hydrocarbons being formed. Also, U.S. Pat. No. 3,928,172 teaches a process for converting hydrocarbonaceous feedstocks wherein olefins are produced by reacting said feedstock in the presence of a ZSM-5 catalyst.
6. Concurrently pending U.S. Ser. No. 09/072,632 discloses a method to improve the yield of propylene by selecting certain reaction conditions and certain catalysts.
Thermal and catalytic conversion of hydrocarbons to olefins is an important industrial process producing millions of pounds of olefins each year. Because of the large volume of production, small improvements in operating efficiency translate into significant profits. Catalysts play an important role in more selective conversion of hydrocarbons to olefins.
While important catalysts are found among the natural and synthetic zeolites, it has also been recognized that non-zeolitic molecular sieves such as silicoaluminophosphates (SAPO) including those described in U.S. Pat. No. 4.440,871 also provide excellent catalysts for cracking to selectively produce light hydrocarbons and olefins. The SAPO molecular sieve has a network of AlO4, SiO4, and PO4 tetrahedra linked by oxygen atoms. The negative charge in the network is balanced by the inclusion of exchangeable protons or cations such as alkali or alkaline earth metal ions. The interstitial spaces or channels formed by the crystalline network enables SAPOs to be used as molecular sieves in separation processes and in catalysis. There are a large number of known SAPO structures. The synthesis and catalytic activity of the SAPO catalysts are disclosed in U.S. Pat. No. 4,440,871.
SAPO catalysts mixed with zeolites (including rare earth exchanged zeolites) are known to be useful in cracking of gasoils (U.S. Pat. No. 5,318,696). U.S. Pat. Nos. 5,456,821 and 5,366,948 describe cracking catalysts with enhanced propylene selectivity which are mixtures of phosphorus treated zeolites with a second catalyst which may be a SAPO or a rare earth exchanged zeolite. Rare earth treated zeolite catalysts useful in catalytic cracking are disclosed in U.S. Pat. Nos. 5,380,690, 5,358,918, 5,326,465, 5232,675 and 4,980,053. Thus there is a need on the art to provide more processes to increase the yields of propylene produced from higher olefin feed stocks such as naphtha feed stocks.
This invention relates to a process to produce propylene from a hydrocarbon feed stream comprising C5""s and/or C6""s comprising introducing the light portion of the feed stream into a reactor containing one or more catalysts separately from the heavy portion of the feed stream, wherein the light portion of the feedstream comprises that portion of the feed stream that boils at 120xc2x0 C. or less, and the heavy portion of the feed stream is that portion left over after the light portion is removed.